The invention relates to the production of a carbon dioxide stream for use in enhanced oil recovery (EOR). The carbon dioxide stream is substantially oxygen-free and fuel-free and is produced from the off gas from underground combustion processes. The invention will also provide for fuel gas streams where nitrogen oxides are also present. The off gas from underground combustion process for oil recovery from bitumen or coal deposits or other fuel gas containing carbon dioxide streams can be the feed gas stream. More particularly, the invention is used in fire flood operations in which oxygen is used as the oxidant with carbon dioxide recycle and a side stream is produced for use in EOR.
EOR applications typically require carbon dioxide concentrations greater than 90, preferably 95% with residual oxygen levels of less than 100 ppmv
When air is used as the oxidant, the off gas from underground fire-flood operation contains only about 15% carbon dioxide together with about 2.5 to 10% of a gaseous fuel, 1% argon and the balance nitrogen on a dry basis as well as sulfur and nitrogen containing impurities derived from coal or oil. The gaseous fuel typically comprises hydrocarbons having from 1 to 6 carbons, carbon monoxide and hydrogen. When oxygen is used as the oxidant, with carbon dioxide recycle, the off gas contains much higher carbon dioxide levels up to about 70 to 85%. In each case, the residual oxygen level is low (not more than about 1%) and excess water and sulfur compounds must be removed before further treatment. Such low heating value streams may have been flared in the past, but this can be damaging environmentally because of the carbon dioxide contained therein and wasteful as no economic benefit is obtained from the fuel present in these streams.
Conventional approaches to remove fuel from the off gas involve adding excess quantities of oxygen before either thermally or catalytically combusting the fuels, optionally recovering at least some of the energy by the generation of steam and/or electricity. In the situation of an oxygen based fire flood, the carbon dioxide concentration is close to the requirements for EOR application after combustion of the fuel but the product then contains 1 to 4% residual oxygen. Although further oxygen may be added to this stream for re-injection into the fire flood operation, the residual oxygen must be removed before any of this stream can be used for EOR. This requires that either the carbon dioxide-containing stream be compressed and liquefied and the carbon dioxide purified up to 99% with some loss of carbon dioxide with the rejected oxygen and other low boiling gases or stoichiometric quantities of hydrogen or another fuel be added and the residual oxygen reacted to water over an De-Oxo catalyst such as palladium on alumina.
NOx removal requires oxidation of NO to NO2 using a supported platinum group metal catalyst or aqueous ozone, followed by caustic scrubbing or selective catalytic reduction (SCR) with a reducing agent such as ammonia. These additional processes add complexity and cost.
Some earlier attempts at partial combustion of fuel from the off-gas from air fired fire flood operation have used platinum containing perovskite combustion catalysts. Sub-stoichiometric levels of oxygen were added to substantially remove the more readily oxidizable carbon monoxide, hydrogen and higher chain hydrocarbon components allowing a methane containing waste stream to be safely vented to the atmosphere. See, for example, U.S. Pat. No. 4,363,361.
A perovskite catalyst supported on a porous substrate has been described for the selective decomposition of N2O in the presence of NO/NO2 at temperatures in the range of 700 to at least 1000° C. that is useful in nitric acid production as detailed in pending U.S. Patent Application Publication No. 2004/179,986.
Exhaust gas can have nitrogen oxides removed by a Pt-group metal containing perovskite catalyst. Exhaust gas containing the nitrogen oxides and steam contact the catalyst at temperatures of 600 to 1000° C. with or without oxygen present and with no reducing agents added without removing moisture from the exhaust gas. See, for example, JP 11342337.
Rare earth perovskite-type catalysts have been used for the catalytic oxidation of NO into NO2. As described in CN 1973962, 80% oxidizing activity is seen at 300° C. Other perovskite catalysts containing metals selected from the group comprising Ru, Pd and Pt have been used for reducing and removing nitrogen oxides where carbon monoxide and unburnt hydrocarbons are present.
Conventional CAR processes have been used in the separation of oxygen and nitrogen from air; syngas production, and other partial oxidation processes. See for example, U.S. Pat. No. 6,059,858; EP 913,184 B1; U.S. Pat. No. 6,379,586; EP 995,715 B1; U.S. Pat. No. 6,761,838; U.S. Pat. No. 6,143,203; U.S. Pat. No. 6,464,955; EP 1,052,219 B1; U.S. Pat. No. 7,070,752; and U.S. Pat. No. 7,303,606.
Cyclic autothermal recovery (CAR) technology makes use of the oxygen “storage” property of perovskites at high temperature. This results in highly selective oxygen extraction from an oxygen containing feed gas, typically air. CAR is based on conventional pelletized materials and employs a cyclic steady state process. Each bed of the perovskite sorbent is alternately exposed to feed air and regeneration gas flows. In one mode, the partial pressure swing mode, using a sweep gas, enables, production of an oxygen-enriched stream for use in oxy-fuel combustion applications. In another mode of operation a fuel containing stream is contacted with the oxygenated perovskite sorbent, thereby generating synthesis gas (hydrogen and carbon monoxide) or other useful chemical products by the partial oxidation reactions or thermal energy by complete combustion of the fuel. Internal regenerative heat transfer is used to maintain the temperature of the perovskite material, the perovskite zone in each bed is sandwiched between two zones of heat transfer material.